There are instances within the field of electronics where screw assemblies are used that require reliable electrical contact between the screw and a receiving threaded female bushing. An example is a tuning screw employed as part of the electrical circuitry in a wireless phone substation radio assembly. These screws must be headless and adjusted up and down many times, each time remaining locked in place. Presently this locking function is achieved by a secondary operation such as gluing, or employing either a lock nut or a spring loaded element to apply a prevailing torque to the screw.
These solutions however are problematic for several reasons. Gluing requires a secondary operation which can be messy. The glue requires a curing time which slows production and the results are often inconsistent. In addition, adjustability and service disassembly is restricted.
The use of a lock nut is also less than desirable because like gluing it requires a secondary operation. A lock nut cannot be used for sub-flush screws and tightening the screw down against the lock nut can inadvertently change the desired position of the screw which must be precisely located.
The use of a traditional nylon locking nut has severe limitations in the electronic tuning screw environment. In a traditional locking bushing a nylon locking washer is located at the top of the nut or bushing to apply a prevailing torque to the screw through frictional engagement with the screw. During engagement the nylon material elastically and plastically deforms into the thread form of the screw. This is unacceptable for electronic tuning screws as there must be metal-to-metal contact between the screw and the bushing to eliminate undesirable electrical capacitive effects. In addition, the applied prevailing torque must be available throughout the full travel of the screw in the bushing.
Another solution that has been tried is the use of axially sprung screws that use thread tension to provide a frictional locking effect however these parts are very difficult to manufacture, are expensive and the number of possible re-use cycles is limited. There is therefore a need in the art for an electronic tuning screw assembly which solves these problems.